The Mosquito. A device that was designed to discourage younger people from loitering outside of buildings. It is based on the fact that older adults exhibit presbycusis, whereas adolescents do not. And here is a news article related to the controversy over the use of such devices.

The vOICe. A device that uses sensory substitution to allow those with vision impairment to see with sound. And here is a news article that shows you how the device works.